4x+6y=8
3x+y=9
y = 9 - 3x
4x + 6( 9-3x ) = 8
4x + 54 - 18x = 8
14x = 46
x = 23/7
y = 9 - 3(23/7)
y = 9 - 69/7
y = - 6/7
To find out we should, divide the whole weight to weight of each pretzels.
The whole is 16 ounce and each pretzel is

ounces. So let's divide :

When you divide a number by a fraction, you can flip the fraction upside down and multiply it with the number, the result will be same.
I cannot answer that, as I do not have the graph and need more info to answer.